Dissolving and regenerating rubber.



Specification of Letters Patent.

Patented May 22, 1906.

Application filed August 10, 1905. Serial No. 2 73,644.

To all whom it may concern.-

Be it known that I, PAUL ALEXANDER, doctor of philosophy and chemist, asubject of the German Emperor, and a resident ofOharlottenburg, in theKingdom of Prussia, German Empire, have invented new and usefulimprovements in processes for the productlon of aqueous caoutchoucsolutions and for the regeneration of rubber waste, of which thefolowing is a full, clear, and exact specificatlon.

It is generally known that caoutchouc, gutta-percha, and similar roductsoccur in nature in the form of so-cal ed milky saps. Milky saps areaqueous liquids which contain liquid bodies insoluble in water in anexceedingly fine state of subdivision. Whether caoutchouc is containedas such in the milky saps of the plants or whether durin the coagulationa change of the original so stances contained in the milky saps takesplace is still an open question.

I have succeeded in converting not only raw caoutchouc, but alsovulcanized caoutchouc material into a condition similar tocaoutchouc-milk. This can be effected by dissolving raw or vulcanizedcaoutchouc in any one of the known solvents, such as hydrocarbons andthe like, and then treating the solution of raw or vulcanized caoutchoucwith a strong alkaline liquid under pressure and stirring. Theoriginally liquid caoutchouc solution is thereby converted into agelatinous condition. If now a solution thus treated be exposed to theaction of a current of steam, the caoutchouc solvent distils off withthe excess of steam, while the water condensing in the rece tacle takesup the caoutchouc material in forming an aqueous solution. The solutionsthus obtained are as regards the condition of the caoutchouc materialprobably not identical with the natural caoutchouc-milk. They give theimpression of colloidal solutions, can be easily filtered, and can beeasily and perfectly freed from mechanical impurities by filterin or bysubsidence. By several subsequent trations it is possible to getsolutions as clear as water. By the addition of acids the caoutchoucsubstance is again separated from the solutions and can then be easilywashedand' brou ht into a useful condition. My solutions 0 eras comparedwith ordinary caoutchouc solu tions the advantage that they can beeasily filtered. Thus, for example, a caoutchouc solution in benzenecan'only be separated mechanically from coarse impurities, finelydividedmineral admixtures not being capable of separation from thesestrongly-viscous solutions, either by filtration or by subsidence. In.consequence hereof solutions containing a large amount of mineralmatters are not only used in caoutchouc manufactures, but are alsobrought into commerce as such, as even after long storage no deposit ofthe mineral substances takes place.

In addition my solutions contain the caoutchouc in a very fine state ofsubdivision and the roducts precipitated therefrom show a very difierentphysical condition, morefavorable to the practical application thereofthan the products obtained from ordinary caoutchouc solutions afterremoval of the solvent. a many-sided application in all cases where itis of importance to mix caoutchouc in a very finestate of subdivisionwith other mediaas, for example, for impregnating fabrics. Ofvery'special advantage is the use of such solutions in the purificationof the raw caoutchouc and in the regeneration of rubber waste. Inparticular n the latter case the possibility of the complete or almostcomplete removal of the mineral constituents is of very greatimportance, for while a regenerated caoutchouc, whichas, for instance,in the American kindsnever contains less than thirty (30) per cent. ofmineral constituents, can of course not be em loyed .to any extent forgood specifically ight mixtures this can be easily done with a productwhich only contains a few percents or only a fraction of a per cent.- ofmineral matters. Bythe abovedescribed process light products which onlycontain fractions of a per cent; of mineral matters can be obtained fromthe specifically heaviest substances.

The following example will explain the process: One thousand (1,000)kilos of caoutchouc waste are heated to one hundred and fifty (150)degrees centigrade, together with three thousand (3,000) kilos ofbenzene, during from three (3) to four (4) hours in a closed vesselunder pressure. 1 The undissolved constituents are then mechanicallyremoved. The solution is returned to the pressure vessel and is heatedto one hundred and fifty (150) degrees centigrade for some time-saythree (3) hours-with two hundred (200) kilos of sodium hydrate in threehundred and fifty (350) kilos of Water. introduced into a retort and istreated with The solution is then condenses inthe vessel.

steam so long as benzene passes off. The steam distillation must beconducted in such manner that a considerable portion of steam Theaqueous solution thus produced is filtered or separated by subsidencefrom mechanical impurities. If it is desired to separate the caoutchoucmaterial from this solution, which can be used' for the above purposes,it is precipitated by the additionof acid or by combustion gases.

Solutions of caoutchouc in an aqueous alkaline solvent were not knownheretofore, and there is consequently no recognized theory by which thetransfer'of the caout- -chouc from the hydrocarbon solvent to thealkaline aqueous solvent can be explained. It

' is believed, however, that during the process first a combination ofthe alkali with the caoutchouc is formed which has the property of beingsoluble in water.

The same process 1s employed when using rawcaoutchouc or other initialmaterials. It

is only necessary to vary the quantity of the solvents and of the alkalisomewhat according to the nature of the material employed. What I claimis 1. The process herein described of producing solutions of caoutchoucin strong alkaline aqueous liquids, which consists in dissolvingcaoutchouc first in one of its well-known sol- I vents, next treating tothe action of steam until the solvent is distilled off from the solutionand the caoutchouc conveyed from the solvent into the aqueous liquid,then se aratirg the impurities con tained in the al aline solution fromthe same, and, lastly, recipitating the caoutchouc from thepurlfiedsolution by means of an acid agent.

3. -A solution of caoutchouc, consisting of caoutchouc dissolved in analkaline liquid.

In testimony that I claim the foregoing as w my invention I have signedmy name in presence of two subscribing witnesses. PAUL ALEXANDER.-

Witnesses:

HENRY HAsPER, WOLDEMAR HAUPT.

